1. Field of the Invention
This invention relates to a process for the preparation of supported, chromium-containing molybdenum and/or tungsten sulfide catalysts, the supported species prepared by such process, and to the use of such supported catalysts for hydroprocessing processes, particularly hydrotreating. More particularly, this invention relates to the preparation and use of supported catalysts useful for hydroprocessing processes such as hydrotreating wherein said catalysts are formed by heating, at elevated temperature, in the presence of sulfur and under oxygen-free conditions, a composite of a support material and one or more precursor compounds selected from the group consisting of (Cr.sub.1-z M.sub.z LX.sub.y)(MoS.sub.4).sub.n, (Cr.sub.1-z M.sub.z LX.sub.y)(WS.sub.4).sub.n and mixture thereof wherein the chromium is in the trivalent state, wherein n=(3-z-y)/2, wherein M is one or more divalent promoter metals selected from the group consisting of Mn, Fe, Co, Ni, Cu, Zn and mixtures thereof, wherein 1&gt;z.gtoreq.0 and 1-z.gtoreq.y.gtoreq.0, wherein L is one or more neutral nitrogen-containing ligands, at least one of which is a chelating polydentate ligand, and wherein X is a singly charged anionic ligand.
2. Background of the Disclosure
The petroleum industry is increasingly turning to heavy crudes, resids, coal and tar sands as sources for future feedstocks. Feedstocks derived from these heavy materials contain more sulfur and nitrogen than feedstocks derived from more conventional crude oils. These feeds therefore require a considerable amount of upgrading in order to obtain usable products therefrom, such upgrading or refining generally being accomplished by hydrotreating processes which are well-known in the petroleum industry.
These processes require the treating with hydrogen of various hydrocarbon fractions, or whole heavy feeds, or feedstocks, in the presence of hydrotreating catalysts to effect conversion of at least a portion of the feeds, or feedstocks to lower molecular weight hydrocarbons, or to effect the removal of unwanted components, or compounds, or their conversion to innocuous or less undesirable compounds. Hydrotreating may be applied to a variety of feedstocks, e.g., solvents, light, middle, or heavy distillate feeds and residual feeds, or fuels. In hydrotreating relatively light feeds, the feeds are treated with hydrogen, often to improve odor, color, stability, combustion characteristics and the like. Unsaturated hydrocarbons are hydrogenated. Sulfur and nitrogen are removed in such treatments. In the hydrodesulfurization (HDS) of heavier feedstocks, or residua, the sulfur compounds are hydrogenated and cracked. Carbon-sulfur bonds are broken, and the sulfur for the most part is converted to hydrogen sulfide which is removed as a gas from the process. Hydrodenitrogenation (HDN), to some degree also generally accompanies hydrodesulfurization reactions. In the hydrodenitrogenation of heavier feedstocks, or residua, the nitrogen compounds are hydrogenated and cracked. Carbon-nitrogen bonds are broken, and the nitrogen is converted to ammonia and evolved from the process. Hydrodesulfurization, to some degree also generally accompanies hydrodenitrogenation reactions. In the hydrodesulfurization of relatively heavy feedstocks, emphasis is on the removal of sulfur from the feedstock. In the hydrodenitrogenation of relatively heavy feedstocks emphasis is on the removal of nitrogen from the feedstock. Albeit, although hydrodesulfurization and hydrodenitrogenation reactions generally occur together, it is usually far more difficult to achieve effective hydrodenitrogenation of feedstocks than hydrodesulfurization of feedstocks.
Catalyst precursors most commonly used for these hydrotreating reactions include materials such as cobalt molybdate on alumina, nickel molybdate on alumina, cobalt molybdate promoted with nickel, nickel tungstate, etc. Also, it is well-known to those skilled in the art to use certain transition metal sulfides such as cobalt and molybdenum sulfides and mixtures thereof to upgrade oils containing sulfur and nitrogen compounds by catalytically removing such compounds in the presence of hydrogen, which processes are collectively known as hydrotreating or hydrorefining processes, it being understood that hydrorefining also includes some hydrogenation of aromatic and unsaturated aliphatic hydrocarbons. Thus, U.S. Pat. No. 2,914,462 discloses the use of molybdenum sulfide for hydrodesulfurizing gas oil and U.S. Pat. No. 3,148,135 discloses the use of molybdenum sulfide for hydrorefining sulfur and nitrogen-containing hydrocarbon oils. U.S. Pat. No. 2,715,603, discloses the use of molybdenum sulfide as a catalyst for the hydrogenation of heavy oils. Molybdenum and tungsten sulfides have other uses as catalysts in reactions such as hydrogenation, methanation, and water gas shift.
In general, with molybdenum and other transition metal sulfide catalysts as well as with other types of catalysts, higher catalyst surface areas result in more active catalysts than similar catalysts with lower surface areas. Thus, those skilled in the art are constantly trying to achieve catalysts that have higher surface areas. More recently, it has been disclosed in U.S. Pat. Nos. 4,243,553 and 4,243,554 that molybdenum sulfide catalyts of relatively high surface area may be obtained by thermally decomposing selected thiomolybdate salts at temperatures ranging from 300.degree.-800.degree. C. in the presence of essentially oxygen-free atmospheres. Suitable atmospheres are disclosed as consisting of argon, vacuum, nitrogen and hydrogen. In U.S. Pat. No. 4,243,554 an ammonium thiomolybdate salt is decomposed by raising the temperature at a rate in excess of 15.degree. C. per minute, whereas in U.S. Pat. No. 4,243,553, a substituted ammonium thiomolybdate salt is thermally decomposed at a very slow heating rate of from about 0.5.degree. to 2.degree. C./min. The processes disclosed in these patents are claimed to produce molybdenum disulfide catalysts having superior properties for water gas shift and methanation reactions and for catalyzed hydrogenation or hydrotreating reactions.
Catalysts comprising molybdenum sulfide in combination with other metal sulfides are also known. Thus, U.S. Pat. No. 2,891,003 discloses an iron-chromium combination for desulfurizing olefinic gasoline fractions; U.S. Pat. No. 3,116,234 discloses Cr--Mo and also Mo with Fe and/or Cr and/or Ni for HDS; U.S. Pat. No. 3,265,615 discloses Cr--Mo for HDN and HDS; U.S. Pat. No. 3,245,903 discloses Fe--Mo and Fe--Co--Mo for lube oil refining; U.S. Pat. No. 3,459,656 discloses Ni--Co--Mo for HDS; U.S. Pat. No. 4,108,761 discloses Fe--Ni--Mo for HDN and U.S. Pat. No. 4,171,258 discloses Fe--Cr--Mo for HDS with steam.